Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $54.42   10.678%   $60.231   $60.23   $60.25   $60.20  
  Purchase #2 $123.98   11.641%   $138.4125   $138.41   $138.40   $138.40  
  Purchase #3 $185.48   5.277%   $195.2678   $195.27   $195.25   $195.30  
  Purchase #4 $72.46   8.427%   $78.5662   $78.57   $78.55   $78.60  
  Purchase #5 $24.99   7.653%   $26.9025   $26.90   $26.90   $26.90  
  Purchase #6 $54.86   13.460%   $62.2442   $62.24   $62.25   $62.20  
  Purchase #7 $60.67   11.614%   $67.7162   $67.72   $67.70   $67.70  
  7 purchase totals = $576.86       $629.3404   $629.34   $629.30   $629.30